Hi Trung;
You might try looking up the alloy phase diagrams of the material you
want to bond to . For silicon, various silicon and germanium alloys
exhibit melting temperatures below 350 C. Also , Tom Eagar of MIT wrote
some articles a few years ago on low temperature eutectic alloys. The
eutectics will melt at much lower temperatures than either material
alone. I found some in a project on low temperature fusion bonding I did
about 5 years ago , but I forget exactly which alloys I used , and I
found them much as I described above.
regards Jdubow